The field of the invention generally relates to washing machines, and more particularly relates to a controller for a washing machine having an alternately reversing drive motor.
Most commercially available, top-loading, agitator type washing machines use an electromechanical timer to control the washing machine automatically through various sequential operations such as water fill, agitate, soak, spin, spin and spray, pause, refill, etc. In the typical arrangement, an electromechanical timer includes a plurality of circumferential rows of timed cams on the outside of a cylinder that is slowly rotated by a small timer rotor. As the cylinder rotates, the cams push in a predetermined sequence against stacked rows of conductor fingers so as to open and close electrical contacts on the fingers. In such manner, the electromechanical timer distributes 120 VAC line voltage in a preprogrammed sequence to various electrical loads such as the motor run windings, the washing machine motor direction selector, and hot and cold water fill solenoids. Various other electrical devices such as an unbalance switch, a lid switch, and a water fill pressure switch are typically connected to the circuit of the electromechanical timer.
In operation, the operator typically first turns a rotary control knob that rotationally positions the electromechanical timer cylinder for the selected washing program such as, REGULAR, PERMANENT PRESS, or DELICATE. Then, upon pulling the control knob out, line voltage is distributed through the electromechanical timer by way of the water temperature selector to the hot and cold water solenoids of the water fill mixer valve. When a pressure sensitive switch toggles in response to the water being filled to a preselected level, the timer motor is energized and the timer cylinder starts to rotate thereby initiating agitation. To accomplish agitation, the electromechanical timer normally applies line voltage for a brief period of time to the resistance start winding of the induction drive motor, and then applies line voltage for the duration of the agitate cycle to the selected high or low speed winding of the motor to drive the input shaft of a reciprocating transmission in one direction. In response thereto, the transmission oscillates the agitator back and forth at a stroke rate such as, for example, 60 strokes per minute. Then, the electromechanical timer applies, line voltage to drive the motor in the opposite direction and, in response thereto, the transmission drives the clothes basket through a spin cycle. Subsequently, other operations such as rinse fill, agitate, and spin are executed under the control of the electromechanical timer in a similar manner to complete the selected washing program.
Electromechanical timers provide a relatively inexpensive and reliable way to distribute line voltage to various washing machine components in a sequentially timed manner so as to execute the preprogrammed operations of various washing programs. Also, electromechanical timers provide a convenient way of integrating control devices such as an unbalance switch, a lid switch, and a pressure fill switch. Further, manufacturers are very familiar with electromechanical timers and their circuits, and users are accustomed to the method and feel of selecting and activating electromechanical timers through the use of a rotary control knob. However, electromechanical timers are generally not suitable for use with a relatively new washing machine technology that uses an alternately reversing motor to eliminate the need for an expensive reciprocating transmission. More specifically, the cam opening and closing rate of conventional electromechanical timers is relatively slow such as, for example, one time every two seconds. However, to drive a reversing motor at a stroke rate such as, for example, 60 strokes per minute, the, line voltage drive to each of the respective stator windings of the motor must be switched at the relatively high rate of 2 times per second. Further, even if the cams of an electromechanical timer could be designed to open and close at a rate of 2 operations per second, the contacts would be subject to a relatively high failure rate. Also, advanced functions such as multiple agitator speeds, multiple spin speeds, and automatic out of balance compensation cannot be performed by a standard electromechanical timer. Such a timer includes no detection and decision making capability other than the decisions exhibited by the slow speed, contact-closing functions.